Pests
Pemphigus fuscicornis (Koch) - Sugar Beet Root Aphid.
Systematic position.
Class Insecta, order Homoptera, superfamily Aphidoidea, family Pemphigidae, subfamily Pemphiginae, genus Pemphigus.Biological group.
Pest of sugar beet.Morphology and biology.
Apterous female is yellowish white, oval-extended, covered with white-bluish wax and albesent, waxy pubescence posteriorly. Head yellow-brown, legs and antennae brown. Eye 3-faceted, red. Body 1.5-2.5 mm in length and 0.7-1.3 mm in width. Parthenogenetic females of summer generations with 5-segmented antennae, unlike those of autumn generations, which have 6-segmented antennae. First-instar larvae (so-called "crawlers") greenish yellow or yellowish gray, with 4-segmented, short antennae, 0.7-0.8 mm in length and 0.2-0.3 mm in width. Initially the species developed holocyclically with heteroecism (alteration of hosts). Primary hosts, most likely, were Narrow-leaf Cottonwood and other species of the subgenus Eupopulus (section of balsamic poplars Tacamahacea), secondary hosts are now represented by some species of herbaceous Chenopodiaceae, primarily lamb's-quarters, goose-foot, and beet (sugar, red, and fodder beet). Alteration of host plants during lifecycle is accompanied by heterogony; interchange of many parthenogenetic generations with viviparous females and one sexual (oviparous) generation. It has been revealed (Mamontova & Doroshina, 1976; Kosmachevskii& Golikov, 1976; etc.), that the Sugar Beet Root Aphid is anholocyclic in Eurasia, inasmuch as it develops only on secondary hosts and is incapable of producing galls and propagating on the native Eurasian poplars of subsection Aegeri (black poplars) as primary hosts. Apterous adults and larvae of various ages overwinter in soil on roots of herbaceous Chenopodiaceae, mainly lamb's-quarters and goose-foot. In spring, the females bear 3-30 1st-instar larvae (crawlers), forming the first summer parthenogenetic generation. Embryos mature simultaneously; larvae are born in a very short time, and, later, the females perish. Summer females live and produce their progeny for a long time, each bearing 28-132 larvae, on average 3-7 larvae every day. First summer generation develops in 9-60 days depending on soil temperature, e.g., 11-19 days at 15-25°C. 9-14 summer generations are produced during growing season. From the end of summer until the beginning of autumn, larvae partly transform into nymphs, developing a late virginoparae (fall migrants), flying out of the beet fields and migrating to poplars. There, in secluded places (under peeling cortex or in fractures of cortex), the virginoparae bear apterous, non-feeding males and oviparous females. After pairing, each female gives birth to only one wintering egg and then dies. In spring, the larvae hatch from overwintered eggs but perish shortly thereafter, unable to form galls on the native Eurasian black poplars. As a result, primary developmental cycle of insect breaks due to absence of late fundatrices that migrate from poplars to herbaceous Chenopodiaceae. Virginoparae appear simultaneously with some larvae, turning into wintering, apterous females. With frosts, summer individuals are able to feed on roots.Distribution.
Nowadays, the species is widespread in all beet-producing areas of the European and Asian regions of the former USSR, i.e., from Moldova and Ukraine to southern Altai, including Transcaucasia (Georgia and Armenia), Kirghizia and Kazakhstan. Before 1959, the insect had not been registered as a pest of beet. It is supposed that earlier the aphid fed on wild species of Chenopodiaceae solely, but the expansion of sugar beet acreage and breakdown of crop rotation created incentives for insect resettlement to beet fields; this for the first time was recorded in Ukraine. In 1960-.70s, there was a very fast dilation of the area invaded by the pest in both developed and new lands, including the Northern Caucasus, Transcaucasia, Central Russia, the Volga region, Kazakhstan and Kirghizia. Outside the former USSR, P. fuscicornis occurs in a number of countries of central, eastern and northern Europe, to southern Sweden and Finland in the North. Morphologically and ecologically, P. fuscicornis is very close to holocyclic P. betae Doane, which inhabits North America.Ecology.
Overwintering occurs in soil at depths from 5 cm to 1 m and deeper, usually 10-30 cm. Spring reactivation starts with warming of soil to 7-9°C or higher. Spreading of the species occurs primarily by very active crawlers. Having found a root of a suitable host plant - e.g., lamb's-quarters, goose-foot, or beet - they go down to secondary roots, where they adhere by suction. Feeding on beet leaves is possible, but only temporarily, as the crawlers either perish or become sterile, even if they survive. Spreading of the aphid occurs along fractures within soil, via tunnels of earthworms, or along soil surface. The larvae searching for host plants are capable of migrating actively along soil surface or passively transported by wind or soil-cultivating mechanisms over long distances. Mass migrations from wild Chenopodiaceae to beet plantings usually take place from June through July and August. The crawlers are most active at night, provided the soil has acquired enough warmth during the afternoon. Reproductive rate of the aphid depends on mechanical structure, humidity, temperature, and aeration of soil. In friable, structured grounds, the aphids are able to move and colonize quickly. Compacted and poorly structured soil is unfavorable for aphid colonization. Heavy wetting (artificial watering or high precipitation) suppresses larval movement. At 23-25°C, females bear 4-12 larvae daily, which turn into adults after 9-11 days. At 17-18°C, females bear 0-3 larvae daily, which turn into adults after 20 days. Absence of accessible hosts (either lamb's-quarters and goose-foot in a field after forecrop harvesting or reseeding spring beet) prevents formation of summer colonization pestholes. Early autumn frosts can reduce aphid numbers sharply. Some biotic factors, such as the fly Thaumatomyia glabra (Mg.), ladybirds, syrphids, lacewings and entomophtorous diseases, have a negative impact on rate of aphid multiplication.Economic significance.
The most obvious sign of Sugar Beet Root Aphid presence is a white, waxy material present on roots and in soil around infested plants. Harmfulness of the aphid becomes apparent gradually. Higher aphid numbers that occur simultaneously with plant stress (i.e. drought) can cause leaf yellowing and growth failure. Secondary roots die, and the main root wilts. Highly infested roots populated by 6,000+ aphids are easily removed from the soil; they often rot, becoming unsuitable for processing or for feeding animals. Damage by Sugar Beet Root Aphid results in root weight losses and reduction of sugar percentage (30-36%). Infestation of beets grown for seed is also dangerous. Control measures include maintenance of crop rotation (the best forecrops are dead fallow, winter wheat, or a vetch-oat mixture); control of weeds from Chenopodiaceae; careful and duly cleaning of harvested beet roots; and the application of pesticides on field border strips during spreading of crawlers. Resistant varieties are popular in the USA as a rather effective tool to control the Sugar Beet Root Aphid.Related references:
Gaponova, A.F. 1977. Trophic relations of sugarbeet root aphid, Pemphigus fuscicornis Koch (Homoptera, Aphidoidea) and its control. Entomol. Obozr. v. 56 (2). p. 292-299 (In Russian)Gaponova, A.F. 1971. Long-term and seasonal population dynamics of sugarbeet root aphid (Pemphigus fuscicornis Koch) and determining factors. In: Zashchita rastenii sakharnoi svekly i drugikh kul'tur ot vreditelei. Kiev. p. 73-85 (In Russian)
Gorbatyuk, N.M. 1973. Influence of ecological factors on development of sugarbeet root aphid. In: Fauna i biologiya nasekomykh Moldavii. Kishinev. p. 106-109 (In Russian)
Doroshina, L.P. 1981. Life cycles of sugarbeet root aphid and it.s near relatives. Kiev: Naukova Dumka. 124 pp. (In Russian)
Kosmachevskii, A.S. & Golikov, V.I. 1976. Sugarbeet root aphid. Moscow: Kolos. 64 p. (In Russian)
Mamontova, V.A. & Doroshina, L.P. 1976. On species affiliation of sugarbeet root aphid (Homoptera, Aphidoidea). Vestnik zoologii 4: 85-87 (In Russian)
Pavlyuk, N.I. 1975. Sugarbeet root aphid (Pemphigus fuscicornis Koch) and biological background of its control in Poltava Region. Summary of Candidate Thesis (Biol. Sci.). Kharkov: Kharkov SKHI. 23 p. (In Russian)
Petrukha, O.I., Gaponova, G.F. & Pisnya I.V. 1976. Control measures of sugarbeet root aphid. Vistnik sil'sko-hospodarsk. nauki 12: 27-29 (In Ukrainian)
Savitskaya, Z.N. 1968. Studying of biological features of sugarbeet root aphid Pemphigus fuscicornis Koch and development of control measures. Summary of Candidate Thesis (Biol. Sci.). Kiev: Ukraine SKHA. 21 p. (In Russian)